1. Field of the Invention
The present invention relates to an engine control apparatus including a computing section performing computation for engine control, and an A/D converting section converting analog signals (sensor signals, for example) into digital signals needed for the computing section to perform the computation for engine control.
2. Description of Related Art
As disclosed, for example in Japanese Patent Application Laid-open No. 2001-265402, there is known a control apparatus for vehicle use which includes a computing ECU (Electronic Control Unit) configured to read in sensor signals, and calculate control data of a given control object from the sensor signals, and a driving ECU configured to drive the control object in accordance with the control data received from the computing ECU through a communication line.
In such a control apparatus, if the control data transmitted through the communication line becomes garbled due to noise, for example, the driving ECU becomes unable to normally control the control object. Accordingly, there has been proposed an added-up value (a sum check value) is added to the end of transmission frame data on the side of the computing ECU, and the driving ECU makes a fault determination on the received transmission frame data by checking whether or not the received transmission frame data and the sum check value match each other, and discards the received transmission frame data if the check result is negative.
Generally, a control apparatus configured to read in sensor signals and perform computation for control purposes like the above computing ECU is provided with an A/D converter which converts sensor signals into digital data and sends the digital data to a computing section including a CPU of the control apparatus. However, the digital data may become garbled in a data transmission line between the A/D converter and the computing section.
Accordingly, it is desirable that the computing section makes a fault determination on the received A/D conversion results (digital data), and if the data is determined to be garbled, the computing section discards the data. This is possible by applying the fault determination process disclosed in the above patent document to the data transmission between the A/D converter and the computing section.
In this case, transmission data including A/D conversion results are added up successively on the side of the A/D converter while the transmission data are being transmitted from the A/D converter, and when all the transmission data have been transmitted, the result of the addition is transmitted as check data from the A/D converter. On the other hand, the transmission data are added up successively while they are being received on the side of the computing section, and a fault determination on the received data is made by comparing the result of this addition with the received check data.
This makes it possible to prevent the computing section from miscalculating a control amount from faulty data (garbled A/D conversion result). Meanwhile, an engine control apparatus which controls a fuel injection amount to an engine and ignition timing, etc., in synchronization with rotation of an engine needs to read in some of sensor signals in synchronization with rotation of the engine, and more precisely, needs to read in each of specific sensor signals while the engine is in a corresponding one of predetermined angular ranges.
For example, in the case where the ignition order of #1 to #4 cylinders of the engine is from #1 to #4, a signal from a first sensor is A/D-converted while the engine is between an ignition TDC position of #1 cylinder and an ignition TDC position of #2 cylinder, and a signal from a second sensor is A/D converted while the engine is between an ignition TDC position of #2 cylinder and an ignition TDC position of #3 cylinder.
When each of the sensor signals from a plurality of the sensors is A/D-converted successively when the engine is in a corresponding one of predetermined angular ranges as exemplified above, since the A/D conversion itself is carried out in synchronization with a clock signal of a fixed frequency, the number of A/D conversion results transmitted to the computing section per unit time varies depending on the rotational speed of the engine, and also the timing or time of completion of transmission of A/D conversion results varies depending on the rotational speed of the engine.
Accordingly, the above engine control apparatus cannot detect garble occurred in the A/D conversion results due to noise or the like on the side of the computing section even if the fault determination process disclosed in the above patent document is used.
In more detail, since it is not possible to determine the timing or time of completion of transmission of a set of A/D conversion results on the side of the A/D converter, because a length of a time period necessary to transmit a given number of A/D conversion results from the A/D converter to the computing section varies depending on the rotational speed of the engine, check data cannot be transmitted in proper timing within a communication time period assigned for transmission of A/D conversion results, and accordingly, it is not possible to detect garble occurred in the A/D conversion results on the side of the computing section.
It might occur that check data is transmitted each time the A/D converter performs A/D conversion. However, in this case, there occurs a problem that switch-over of sensor signals in the A/D converter is delayed, causing a timing of start of A/D conversion and also a timing of start of transmission of A/D conversion result to be delayed.
Particularly, when the rotational speed of the engine is high, and accordingly the length of a communication time interval assigned to the respective sensors is short, it becomes difficult to ensure a time sufficiently long for performing A/D-conversion and transmitting A/D conversion result, causing interruption of transmission of A/D conversion results from the A/D converter to the computing section.